In order to become allergic to such a substance, one must have had at least one previous exposure that eventually triggers an immune response.

This dermatitis is not caused by an antibody but is due to a cellular immune response mediated by a type of blood cell (T-lymphocytes) that has surface molecules that enable it to recognize specific small chemical allergens.

When these lymphocytes come in contact with the allergen, they release a variety chemicals that are able either directly or by stimulating other cells produce an itchy dermatitis.

Typically, this sort of reaction occurs only on the skin and requires at least 24 to 48 hours to develop.

Common plants that produce allergic contact dermatitis include poison ivy, poison oak, and poison sumac of the
Anacardiaceae family. The allergenic chemical is present in the sap or latex that contaminates damaged stems or leaves.

Many other substances can cause allergic reactions, including components of hair dyes or straighteners; metallic nickel in jewelry and belt buckles; leather tanning agents; and chemical additives to latex rubber.

The fragrances in soaps and preservatives and emulsifiers in shampoos, lotions, perfumes, and cosmetics can cause reactions.

Medications applied to the skin, like neomycin (Mycifradin, Neo-Fradin, Neo-Tab), are a common cause of this type of dermatitis.

Irritant contact dermatitis results from coming in contact with a substance that directly damaging and irritating to your skin. No allergy is required, and it will occur on the first exposure.

The longer the substance remains on the skin, the more severe the reaction.

Many chemicals, including industrial cleaning products and solvents, can cause this condition.

Household cleaners such as detergents can also cause dermatitis.

People with other skin conditions, such as eczema (atopic dermatitis), are more likely to develop contact dermatitis.